(1) Field of the Invention
The present invention relates to methods used to fabricate semiconductor devices, and more specifically to an ion implantation procedure, used to improve the reliability of metal oxide semiconductor field effect transistor, (MOSFET), devices, in regards to a hot electron carrier phenomena.
(2) Description of Prior Art
Micro-miniaturization has allowed the semiconductor industry to fabricate MOSFET devices with sub-quarter micron features. Specific MOSFET devices, such as input/output, N channel, (I/O NMOS), devices, used for logic applications, can however be prone to a hot electron carrier, (HCE), reliabiltty phenomena. The I/O NMOS devices, operating at a voltage of 3.3, or 2.5 volts, can suffer gate insulator degradation, as a result of hot electron injection at these operating voltages. The substrate current, or drain current specifications are therefore difficult to satisfy, as a result of the HCE phenomena, for sub-quarter micron, I/O NMOS devices, operating at 3.3, or 2.5 volts. Methods of anmealing the gate insulator layer, in an NO or N.sub.2 O ambient, have not resulted in reductions in substrate current, (Isub), while other methods such as only providing a more graded, lightly doped source/drain, (LDD), region, have also not delivered the improved reliability of I/O NMOS devices, regarding HCE injection.
This invention will describe a novel process used to alleviate HCE injection, entailing the implantation of nitrogen, (N.sub.2), or nitrogen ions, (N.sup.+), either prior to, or after deposition of a silicon oxide layer, obtained using tetraethylorthosilicate, (TEOS), as a source, with the TEOS layer used as a liner layer, prior to formation of composite insulator spacers. The nitrogen implantation, located adjacent to the gate structure, and at the interface of a silicon oxide layer, underlying the composite insulator spacer, and an underlying lightly doped source/drain region, reduces HCE injection, as a result of nitrogen pile-up, at this interface. In addition the unplantation procedure allows an increase in transient enhanced diffusion, (TED), to occur, resulting in a greater degree of LDD grading, than offered by counterparts fabricated without this nitrogen implant, thus reducing Isub, indicating a reduction of HCE injection. Prior art, such as Gardner et al, in U.S. Pat. No. 5,994,175, as well as Arai et al, in U.S. Pat. No. 5,972,783, describe nitrogen implantation prior to LDD formation, not however describing this present invention of implanting nitrogen, post LDD implantation, performed either prior to, or after deposition of a TEOS liner, used underlying a subsequent composite insulator layer.